1. Field of the Invention
The invention pertains to an operating device for a forward moving looper in sewing machines of the type in which the needle has work feeding movements. In such machines the orbital movement of the fabric feed dog is synchronized with an analogous movement of the machine's needle and, to assist in the transport of the fabric, it is caused to penetrate the latter and to be displaced simultaneously with the feed dog.
2. Description of the Prior Art
In machines in which the needle has a work feeding movement, the length of the stitch of a seam can be adjusted from zero up through intermediate values to a maximum value. When the stitch length is zero, the feed dog only performs a raising and lowering movement, the needle follows a vertical trajectory and the looper performs an oscillating movement thereby its tip is at a pre-established distance from the vertical which passes through the lower dead point of the needle.
When the sewing machine is set up to produce a certain stitch length, both the needle and the feed dog, being synchronized, are caused to be displaced simultaneously so as to effect transport or advance the fabric. A problem, however, exists with such sewing machines for the looper continues to form the stitches in a conventional manner regardless of machine set up for a particular length stitch and at whatever position the needle is withdrawn relative to the vertical that passes through the lower dead point of the needle.
Sewing machines of the type described supra are well known to those conversant in the art and an example of one such machine is shown and described in U.S. Pat. No. 2,266,140. The teachings of this patent show and describe a device for operating a looper at a variable velocity which is effective in increasing the velocity of the looper when necessary so that its tip will seize the loop of needle thread. With this arrangement, the transport movements of the machine's needle are also variable. Although the mechanisms of this patent have performed their intended functions with a degree of satisfaction, they possess what is considered an extremely complicated arrangement of elements having limitations under certain conditions which do not consistently provide for the seizure of the needle thread loop.
Another sewing machine of the type referred to above is shown and described in U.S. Pat. No. 3,285,210. The teachings of this patent disclose an apparatus which satisfactorily performs its intended function but, unlike the present invention, it is necessary that the operating device for the looper be regulated each and every time it is desirable to vary the stitch length in a machine as well as when the transport movements of the needle are varied. In addition to this required regulation of the looper operating device, it is only possible to obtain stitch lengths of predetermined value and not intermediate values as is available with the device according to the invention. The invention provides an operating device for a sewing machine looper having forward movements and a needle that is provided with work feeding movements. The device includes means for simultaneously and adjustably operating the feed dog and needle during their work feeding movements and for causing the looper to oscillate. This oscillating is initiated in a manner whereby, upon an increase in stitch length, the start of the arc made by the point of the looper is moved away from the vertical passing through the lower dead point of the needle. With a decrease in the stitch length, the start of the arc made by the point of the looper is caused to move towards the vertical passing through the lower dead point of the needle and the displacements toward and away from this vertical define the extent proportional to the selected stitch length.